This was really confusing for me as a teenager, and it’s probably the single most important thing that held my sports performance back in high school. People were always telling me I wasn’t being aggressive, and it seemed like they were telling me to foul the other guy as much as possible without being penalized for it. The idea of cheating a little bit didn’t make any sense, because where do you draw the line? Clearly you aren’t supposed to kill the guy and make it look like an accident*. It seemed arbitrary, and therefore ambiguous, and therefore confusing for an autistic person.
Well, now that I’m old and wise I can tell you…there’s one other little detail, but I essentially had it right back then. The other thing is to not foul the other guy enough to provoke retaliation. The game theory of interacting expectations** about how much fouling is too much provides some protection against violence purity spirals. There are reasons for all this related to the meta-games around why humans play sports (and in-group competition generally), but if you just want to learn the dynamics of the etiquette for the purpose of surviving the social meta-game, start here: https://www.amazon.com/dp/B009N36GCQ/ref=dp-kindle-redirect?_encoding=UTF8&btkr=1
*Popular opinion starts edging that way at the very top levels when professional sports starts crossing over with political identity and big money. At that point you’re playing the social meta-game of geopolitics, and the general rule there is anything goes as long as you don’t get caught.
**I like to think of these recursive social expectation games as “expectation dances”. They tend to produce homeostasis toward the crowd wisdom’s evaluation of the meta-game, which is pretty impressive from an anthropological perspective. In less clinical terms, if the kids are getting so rough it’s hurting the group interests people get upset, and if the kids aren’t getting rough enough to serve the group interests people get upset.